Actually, I'm going to submit that there's no reason, but there's no EVIDENCE that there's no problem.
You may just needlessly dilute the add packs by doing that, Brett.
If you're trying to thicken the brew, remember that most oils have a dramatically different add pack in 5W20 than in 5W30, so blending within brands across the SAE 20-30 barrier may not even keep you in the same chemistry.
Theories of formulation also sometimes differ between different lines of oil from the same blender...
That being said, dollars to donuts this blend will go 7500 miles under normal driving conditions. I wouldn't really be inclined to take PP out to extreme extended drains until we have more evidence that it can retain its TBN to 10K and beyond. I like to see a TBN of 6 or so at 10K to know an oil can make it to 15K...
